Many of today's computing devices, such as desktop computers, personal computers, and mobile phones, allow users to perform audio processing on recorded audio or video clips. These computing devices may have audio and video editing applications (hereafter collectively referred to as media content editing applications or media-editing applications) that provide a wide variety of audio processing techniques, enabling media artists and other users with the necessary tools to manipulate the audio of an audio or video clip. Examples of such applications include Final Cut Pro® and iMovie®, both sold by Apple Inc. These applications give users the ability to piece together different audio or video clips to create a composite media presentation.
Dynamic range compression is an audio processing technique that reduces the volume of loud sounds or amplifies quiet sounds by narrowing or “compressing” an audio signal's dynamic range. Dynamic range compression can either reduce loud sounds over a certain threshold while letting quiet sounds remain unaffected, or increase the loudness of sounds below a threshold while leaving louder sounds unchanged.
An audio engineer can use a compressor to reduce the dynamic range of source material in order to allow the source signal to be recorded optimally on a medium with a more limited dynamic range than that of the source signal or to change the character of an instrument being processed. Dynamic range compression can also be used to increase the perceived volume of audio tracks, or to balance the volume of highly-variable music. This improves the listenability of audio content when played through poor-quality speakers or in noisy environments.
Performing useful dynamic range compression for audio content requires the adjustment of many parameters such as a noise gate threshold (noise gate), a dynamic range compression threshold (threshold), and a dynamic range compression ratio (ratio). In order to achieve a useful dynamic range reduction, one must adjust the threshold parameter and the ratio parameter so that the audio compressor achieves the desired dynamic range compression with few obvious unpleasant audio effects. One must also adjust the noise gate parameter to avoid letting too much noise through and to avoid attenuating too much useful audio. The adjustment of these and other parameters requires sufficient knowledge in acoustics, or at least several rounds of trial-and-error by a determined user.
What is needed is an apparatus or a method that determines and supplies a set of audio dynamic range compression parameters to an audio compressor, and a method or apparatus that automatically computes the noise gate, threshold, and ratio parameters so that the user of a media editing application can quickly and easily accomplish useful dynamic range compression on any given audio content.